He likely is learning the C model, PM.
The thing about the UNS-1 is that it's pretty much user-friendly, but you need to USE it in order to KNOW it. Way back when, I read the book on the UNS-1 and thought I then knew the box. Got in the plane (Learjet 55 with UNS-1M) and... was completely lost.
In order to really know how to use even the most basic aspects of the UNS-1 (like loading a flight plan) it really takes practice. If you happen to be going for a type rating a lot of the schools do have a training device that allows you to practice without having to waste valuable sim time banging your head on the glare shield because you can't load the departures, arrivals and approaches you'll be "flying."
Practice, practice, practice...